1. Field of Invention
The present invention relates to compositions and methods for removing silicon nitride and silicon dioxide at about the same removal rate by chemical-mechanical polishing.
2. Description of Related Art
Silicon nitride is widely used as a barrier layer and/or as an etch stop layer to protect underlying devices from being removed during chemical-mechanical polishing (CMP) in integrated circuit (IC) fabrication. Accordingly, most CMP polishing slurries and processes have attempted to minimize the silicon nitride removal rate while attaining relatively high removal rates for other layers. CMP polishing slurries and processes that are highly selective for silicon dioxide in preference to silicon nitride have been developed and utilized in the shallow trench isolation (STI) manufacturing process.
There are emerging technologies in the semiconductor industry where it would be advantageous to have CMP slurries and processes whereby the removal rate of silicon nitride is about the same as the removal rate of silicon dioxide. Suppressing the silicon dioxide removal rate while at the same time achieving a substantially equal silicon nitride removal rate is immensely challenging because the removal of silicon nitride via CMP typically follows a mechanism in which the surface of the silicon nitride is hydrolyzed to silicon dioxide (Si3N4+6H2O→3SiO2+4NH3), which is then removed during CMP. Accordingly, additives conventionally used in CMP slurries to suppress the silicon dioxide removal rate tend to suppress the silicon nitride removal rate because the silicon nitride is converted to silicon dioxide and removed as such.